Children with autistic spectrum disorder (ASD) who undergo a regression of language abilities are said to have autistic regression. Preliminary evidence suggests that subclinical epileptic activity may be a potential cause of autistic regression. Our specific aim is to determine if young children with ASD and regression have more epileptiform EEG abnormalities than young children with ASD and no regression. To increase the yield of the EEG recordings, the patients will be admitted to the PCRC overnight for a 12 hour sleep recording.